Parochially known as "Special K," "Vitamin K," or simply "K," ketamine is a conger of phencyclidine (PCP). Used for many years as an anesthetic in emergency and veterinary medicine, ketamine has recently emerged in a non-clinical context as one of several synthetic substances classified as "club drugs." Like other so-called "club drugs," such as MDMA, GHB, and Methamphetamine, most available information about ketamine stems from studies focused on "club drug" environments and populations, notably MSM venues. Much of this data has presumed non-injected modes of administrating ketamine, and HIV risk has been assessed in relation to increased risk for sexual transmission. However, pilot data from our R03 study indicates that ketamine is prevalent among non-MSM populations and venues, notably in diverse sub-populations of high risk youth. Moreover, pilot data also indicate the previously unrecognized use of injection as a mode of administration. While ketamine injection practices have yet to be systematically described, preliminary data indicate the use of an array of drug preparation and injection techniques that may pose increased risk for transmission of blood-borne pathogens, notably HIV-1, HBV, and HCV. Following a comparative research design that we have successfully applied in previous studies of out-of-treatment populations, we propose a descriptive epidemiological study of ketamine injection among high risk youth in three cities - New York City, New Orleans, and Los Angles. We will employ methods of ethnographic observation to develop a systematic description of the behavioral practices used to prepare and inject ketamine. Following our prior work in modeling injection practices, we will identify discrete features of ketamine injection that may exacerbate or attenuate risk for viral transmission, including variability in these practices that may be associated with different forms of ketamine and various of patterns of ketamine acquisition. Finally, we will recruit a cohort of high risk youth in NYC who have recently initiated injection of ketamine and describe the social course and unintended medical consequences associated with the use of injection as a mode of administration.